I think there are two concerns here. If this works correctly on Windows, which could mean different things, freetype would be interested I think in fixing this as well, depending on how this is broken exactly. I think it's worth reporting.
Regarding LOAD_PEDANTIC, I don't think I ever used that. Any idea what would be potential performance impact? Does it enable some validation incrementally, or is everything validated at every Load_Glyph() call.